The present invention relates to systems to detect rotational characteristics of a mechanical member, and more particularly, but not exclusively, relates to a sensor arrangement to detect a rotational characteristic of an engine crankshaft or camshaft.
With the advent of electronically controlled internal combustion engines, devices to detect rotation of the engine crankshaft or camshaft have become increasingly popular. For example, angular position of the crankshaft or "crank angle" is frequently sensed to control engine fueling, ignition, and exhaustion. Also, engine speed, as indicated by rotational speed of the crankshaft, is often an important parameter in various engine control system schemes. U.S. Pat. Nos. 5,476,082 to Carpenter et al., 5,361,630 to Kowalski, and 4,936,277 to Deutsch et al. are cited as general sources of background information relating to various electronic engine control systems which rely on measurement of crankshaft rotation.
In order to meet increasingly rigorous emission standards imposed on vehicles with internal combustion engines, crank angle needs to be measured with high precision. One way to provide the needed precision is to employ a crank angle detection system that has a sensor and a reference member which rotates with the crankshaft adjacent the sensor. The sensor is configured to detect rotation of the reference member.
One type of detection system has a reference member with several angularly spaced indicators, or "angle marks," along its periphery which are configured to alter a magnetic field. As each one of these indicators moves past the sensor, the sensor detects the corresponding alteration of the magnetic field and generates a detection pulse. By varying the spacing of the indicators in a known manner, an index to the relative angular position of the crankshaft may be provided. Also, the rate of these pulses may be used to determine rotational speed of the crankshaft. U.S. Pat. Nos. 5,520,043 to Koelle et al., 5,469,823 to Ott et al., 5,460,134 to Ott et al., 4,760,827 to Schreiber et al., 4,442,822 to Kondo et al., and 4,365,602 to Stiller et al. are cited as examples of various types of crank angle detection systems.
In one crank angle detection system arrangement, a reference disc is attached to a transmission fly wheel external to the engine. Unfortunately, external placement of the disc usually requires a separate design effort for each different type of transmission offered with a given engine design. Therefore, in many instances it is desirable to provide the reference disc as part of the engine. However, attaching the disc directly to the crankshaft generally requires lengthening the crankshaft to provide an appropriate attachment site.
U.S. Pat. No. 5,361,630 to Kowalski discloses one attempt to solve this problem by integrally forming indicator slots on a crankshaft counter weight which then serves as a rotational reference member. Unfortunately, this approach still requires an extensive re-design of the crankshaft. Also, the integral counter weight design requires disassembly of the crankshaft should replacement or adjustment of the reference member be required.
Thus, there remains a need for a crankshaft rotation detection system that can be readily adapted to different engine configurations. The present invention satisfies this need.